A mechanism of this type, similar to that which forms part of certain watch movements that are already manufactured and marketed by the Applicant is shown in an exploded perspective view in FIG. 1, as well as other elements of the movement which are directly related to this mechanism.
Among these elements there is an hour wheel 2 mounted at the centre of the movement and making one revolution in 12 hours, the pipe 4 of which is for carrying an hour hand that is not shown.
A pipe 6 of a minute wheel, itself surrounding an axis 8 of a second wheel, can rotate inside this pipe 4, said pipe 6 and said axis 8 being provided for respectively carrying a minute hand and a second hand which are also not shown.
On pipe 4 of hour wheel 2 and in contact with said wheel there is fixed a pinion 10 with six teeth 12, which meshes with a drive wheel 16. In order to make one revolution in 24 hours, this drive wheel, which pivots about a fixed arbour 14 of the movement and which includes twelve teeth 18, is solely responsible for driving both a day of the week disc 20 secured to a day star-wheel 22 and a date crown 24, in a manner that will be explained hereinafter.
Among the elements of the movement directly related to the date mechanism there is also a plate 26 that is partially shown, which includes an upper edge 28 that acts as a support for a dial 30 provided with an aperture 32. This plate 26 which allows dial 30 to be axially positioned, is also used for positioning it angularly by means that are not shown, such that its aperture 32 is located at 3 o'clock to allow the user of the watch containing the movement to read the day of the week and the date of the day correctly through the aperture.
Moreover, plate 26 also acts as a support for date crown 24, which is surrounded and held in place radially by edge 28 of the plate.
As the drawing shows, the day disc 20 which carries abbreviations of the seven days of the week twice in the same language and the day star-wheel 22 which consequently includes fourteen teeth 34, are mounted so as to be able to pivot about pipe 4 of hour wheel 2 and held in place axially by a key 36, the assembly of disc 20 and star-wheel 22 being able to be achieved for example by riveting or laser welding.
As regards date crown 24, which can be obtained by cutting and folding a sheet metal or a thin metal strip, it has a stair shaped profile and includes three concentric annular parts 38, 40 and 42, whose level decreases from the outside inwards.
The first annular part 38, whose contour corresponds to that of the crown, carries numbers from 1 to 31 regularly distributed over its surface. The second part 40, which receives day disc 20, has a slightly larger diameter than that of the disc so as not to disturb its rotation and the difference in level between this second part and the first is such that the day of the week and the date appear substantially in the same plane and close to each other in aperture 32 of dial 30. Third part 42 has an inner toothing which includes 31 radial teeth of isosceles shape 44 which correspond to the 31 days of the longest months.
The calendar mechanism of the movement of FIG. 1 also includes a holding plate 46 inserted between day disc 20 and third part 42 of date crown 24, which is fixed by means of screws 48 to a fixed part of the movement. This plate 46 has three functions. The first and second consist in holding drive wheel 16 and date crown 24 axially without disturbing their mobility. The third function is to act as jumper-springs for date crown 24 and for day star-wheel 20. In order to do this, plate 46 is cut and bent so as to form a first elastic tongue 50, which extends below the plane of the main part of the plate and which ends in a V-shaped end, pointed towards the exterior of the movement to be engaged between teeth 44 of date crown 24 and a second elastic tongue 52 extending above the plane of said plate 46 and which also ends in an end part that is V-shaped, but pointed towards the inside of the movement to be engaged between teeth 34 of day star-wheel 22, which are both radial and isosceles shaped.
In order to describe drive wheel 16 and the operation of the calendar mechanism of FIG. 1 in detail, reference will also be made to FIG. 2, which shows wheel 16 in perspective again but on a larger scale.
This wheel 16 includes a hub 54 via which it is mounted on arbour 14 and which is connected by a spoke-shaped connecting element 56 to a crown 58 which carries the aforementioned teeth 18.
Among these teeth 18 there is a prominent tooth 18′ which extends radially beyond the others so as to be the only one able to be engaged between teeth 44 of date crown 24 while being able to be engaged like the others between teeth 12 of pinion 10. For a reason that will be understood hereinafter, this tooth 18′ has a flank called the “front flank” 60 of the same inclination as the flanks of the other teeth, i.e. substantially radial, and a “back flank” 62 which, at the end of the tooth intended to be engaged between teeth 44 of crown 58 has an oblique face 64 of smaller inclination to form an acute angle with front flank 60.
This having been said, wheel 16 also includes an elastic arm 66 more or less shaped in the arc of a circle, integral with the other elements of wheel 16, attached to hub 54 and extending inside toothed crown 58. This arm has, at its free end, a first tongue of substantially rectangular shape and bent at 90° towards the front of the movement so as to form a drive finger 68 able to be engaged between teeth 34 of day star-wheel 22. Moreover, arm 66 and the orientation of drive finger 68 with respect to the flanks of teeth 34 are provided such that the arm is only deformed significantly when it is forced to move away from hub 54 of wheel 16 and very slightly in the opposite direction.
Finally, wheel 16 also includes a second tongue 70 of substantially rectangular shape, made in one piece with elastic arm 66, located in the plane of the wheel, at a certain distance from the end of the arm and extending in the direction of crown 58. The usefulness and advantage of this second tongue which is not involved in the operation of the calendar mechanism of FIGS. 1 and 2, will be specified hereinafter.
The calendar mechanism of FIGS. 1 and 2 is of the dragging type, i.e. the movement of the date forward one unit and passage from one day of the week to the next occur over a period of approximately four hours around midnight.
While the movement is operating normally, outside this time period, its motor, whether it is of the purely mechanical or electromechanical type, drives pinion 10 in the clockwise direction and calendar drive wheel 16 in the anti-clockwise direction indicated by arrow F1 in the drawing. During this time period, wheel 16 does neither mesh with date crown 24 nor with day star-wheel 22 whose positions are determined and maintained by jumper-springs 50 and 52 such that the indications of the date and day of the week appear properly framed in the aperture of dial 30 and without any shocks that the movement undergoes being able to alter said indications.
For a reason that will be explained hereinafter, drive wheel 16 is designed such that there is a certain phase shift, for example of approximately half an hour, between the start of driving day disc 20 and that of date crown 24 or conversely. Hereinafter, it will be assumed that we are in the first of these situations to describe the operation of the calendar mechanism of FIGS. 1 and 2 and a variant thereof that is also known and that of the mechanism according to the invention.
In these circumstances, when drive finger 68 comes into contact with the back flank of a tooth 34 of day star-wheel 22, the finger starts to exert a torque on said tooth 34, which is opposed by the action of jumper-spring 52. Gradually as drive wheel 16 rotates in the direction of arrow F1, elastic arm 66 becomes taut moving away from hub 54 and finger 68 slides along the flank of tooth 34 with which it is in contact and rotates star-wheel 22 and day disc 20 in the direction of arrow F2. At the same time, the end of jumper-spring 52 comes out of the hollow between two teeth of star-wheel 22 in which it was located, while the torque exerted by finger 68 on tooth 34 increases.
Approximately half an hour after the star-wheel and the day disc start to be driven, front flank 60 of tooth 18′ of wheel 16 comes into contact with the back flank of a tooth 44 of date crown 24 and then starts to slide over this back flank and to rotate the date crown in the direction of arrow F3, i.e. in the same direction as drive wheel 16 and in the opposite direction to that in which day disc 20 is rotating. During this time, the end of jumper-spring 50 starts to come out of the hollow between two teeth 18 of the date crown in which it was located, said spring starts to tighten and the torque exerted by tooth 18′ on tooth 44 with which it is in contact starts to increase.
During the period that follows, which is the longest of the time interval necessary to change the day and the date, wheel 16 simultaneously drives day star-wheel 22 and date crown 24 supplying a higher torque than that of the sum of the resistant torques exerted by jumper-springs 50 and 52 respectively on tooth 34 of day star-wheel 22 and that 44 of date crown 24 with which tooth 18′ and tooth 34 of day star-wheel 22, these torques continuing to increase until the end of jumper-spring 52 reaches the tip of tooth 34 of day star-wheel 22.
In a very short instant, spring 52 is let down when its tip descends into the hollow of day star-wheel 22 following that between the teeth of which it was previously located, in the direction of arrow F2. At the same moment, drive finger 68 of arm 16 is ejected from the toothing of day star-wheel 22 while it was exerting a maximum torque on the latter and the day of the week indicated by disc 20 finishes passing to the next day.
A little later, the same process occurs for jumper-spring 50, the hollow between teeth 44 of date crown 24 between which its end was located and long tooth 18′ of drive wheel 16, which means that the date indication moves forward one unit.
Thus, owing to the phase shift between driving the day disc and that of the date crown, the total torque provided by the drive wheel 16 never reaches the sum of the maximum torques exerted by said wheel on the day star-wheel and the date crown, which prevents the movement drive motor locking or at lest the disc and/or the crown moving backwards.
When an alteration of the date indication in particular during passage from a month of thirty days or less in the case of February to the next month, or an alteration both of the date and the day of the week indication, for example when the battery is changed in the case of an electromechanical movement or an extended lack of winding in the case of a mechanical watch, this or these changes can occur manually and quickly by means of a control stem and a correction mechanism that are not shown in the drawing. In the case of movements marketed by the Applicant, as in many others, the control stem is a stem which can be placed in three axial positions, a neutral or winding pushed-in position, a first pulled out position in which the date display can be altered by rotating the stem in one direction and the day of the week display by rotating the stem in the other direction and a second pulled out position reserved for setting the time of the hands of the watch.
When the date is set outside the time interval when neither the day disc nor the date crown are being driven by wheel 16, this does not cause any problems. However, very often, setting the day and more frequently setting the date occurs around midnight, i.e. during this interval.
When an alteration of the date occurs in these circumstances, the date correction mechanism non shown acts on teeth 44 of date crown 24 so as to rotate the latter in the direction of arrow F3, against jumper-spring 50 and each time that the front flank of a tooth 44 comes into contact with the oblique face 64 of the back flank of tooth 18′ of drive wheel 16, this front flank of a tooth 44 slides over this oblique face of tooth 18′ without substantially altering the angular position of tooth 18′, owing to the natural elasticity drive wheel 16 which is then very slightly deformed and against the resistant torque then exerted on said wheel 16 by pinion 10, which rotates in the opposite direction at a much lower speed, which can even be considered to be zero.
In the case where, more rarely, the position of the day disc also has to be altered during the time interval in question, the correction mechanism drives day star-wheel 22 in the direction of arrow F2 making the end of jumper-spring 52 jump from a hollow between two teeth 34 to the next one. When a front flank of a tooth of day star-wheel 22 comes into contact with drive finger 68, it forces elastic arm 66 to curve very slightly in the direction of hub 54 of wheel 16 to return then to its initial position after finger 68 has passed to the tip of tooth 22.
Moreover, if the time is altered forwards, everything occurs in the same way as when the mechanism is operating normally, except that if this alteration occurs while the day and date change process is in progress, this process is accelerated during the period in which the time is being altered. However, if the time change occurs backwards, wheel 16 rotates in the opposite direction to that of arrow F1. In this case, when oblique face 64 is or comes into contact with a tooth 44 of the date crown, this tooth slides or continues to slide over this face, which causes or maintains a slight deformation of the crown of wheel 16 which means that the position of the wheel remains unchanged. When, during the same period, the back face of tooth 68 comes into contact with a tooth 34 of day star-wheel 22, this tooth slides over the back face which only causes a very slight deformation of arm 66 in the direction bringing it back to hub 54 of the wheel until tooth 68 reaches the tip of tooth 34. At that moment, the arm returns to its initial position without the position of star-wheel 22 and day disc 20 having been altered.
FIGS. 3 and 4 illustrate a variant of the calendar mechanism shown in FIGS. 1 and 2, which corresponds to a mechanism used in other movements, also manufactured and marketed by the Applicant.
As shown in FIG. 3, which is a top view of the day of the week disc and the day star-wheel, this star-wheel still being designated by the reference numeral 22 remains unchanged and still includes fourteen teeth 34.
However, day disc 20′ no longer carries abbreviations of the successive days of the week twice in the same language, like disc 20 of FIG. 1, but alternatively, the abbreviations of the days in two languages, in this particular case, in English and French.
Consequently, in order always to have the day displayed in the same language, the day star-wheel and disc must no longer rotate normally by one fourteenth of a revolution per day, but by a seventh. In order to do this, the second tongue 70 of drive wheel 16 shown in FIGS. 1 and 2 simply has to be bent to make a second drive finger 70′, as shown in FIG. 4. Thus, after first finger 68 has acted on a tooth 34 of day star-wheel 22 to rotate day disc 20′ by a fourteenth of a revolution, second drive finger 70′ acts in the same way on the following tooth 34 to rotate the disc again by a fourteenth of a revolution in the same direction.
As for first finger 68 and for the same reason, the action of second finger 70′ is synchronised with that of tooth 18′ so that the total torque that drive wheel 16 has to exert at the same time on day star-wheel 22 and date crown 24 never reaches the sum of the maximum torques necessary to rotate the star-wheel and the crown.
Moreover, when the day of the week is changed manually, second finger 70′ acts like first finger 68, i.e. it forces elastic arm 66 to curve to allow star-wheel 22 and day disc 20′ to pass to the display of a same day in one language to another, or from one day to the next in the same language.
Naturally, everything that has previously been said with respect to first drive finger 68 and arm 66 is also valid for second drive finger 70′.
Furthermore, this variant of FIGS. 3 and 4 justifies the presence of tongue 70 in the embodiment of FIGS. 1 and 2. In fact, in order to make drive wheels 16 that can be used in both cases, one need only cut flat parts having the two tongues for forming the two drive fingers 68 and 70′ from a metal strip or plate, and bend only one of the tongues or both to obtain wheels which can be used either in the embodiment of FIGS. 1 and 2, or in its variant, which evidently constitutes a saving.
Despite this, this embodiment of FIGS. 1 and 2 and its variant have certain drawbacks.
First, wheel 16 made in a single piece of the same material does not allow optimum driving of both the day star-wheel and the date crown to be obtained as a function of the materials of which they may be formed, for example when the date crown is made of a copper and beryllium alloy whereas the day star-wheel is made of steel to allow a day disc to be laser welded onto said star-wheel.
Secondly, for a given movement, the phase shift sign and value between the driving of the day disc and that of the date crown are determined when drive wheel 16 is designed and manufactured. For various reasons, it may be preferable to start by driving the date crown rather than the star-wheel and the day disc and not necessarily with the same forward movement. In the case of the known mechanisms of FIGS. 1 to 4, this can only be achieved by replacing wheel 16 with another wheel.
Finally, thirdly, in these known mechanisms of FIGS. 1 to 4, drive wheel 16, which is actually very thin, has to drive both the date crown and the day star-wheel for a long time in opposite directions, which means that it is then subjected to quite significant stress which can greatly limit is life time and the proper operation or even just the operation of the calendar mechanism of which it forms a part.